Geology Reference
In-Depth Information
Elements of Map-Scale Structure
1.1
Introduction
The primary objective of structural map making and map interpretation is to develop an
internally consistent three-dimensional picture of the structure that agrees with all the
data. This can be difficult or ambiguous because the complete structure is usually
undersampled. Thus an interpretation of the complete geometry will probably require a
significant number of inferences, as, for example, in the interpolation of a folded surface
between the observation points. Constraints on the interpretation are both topological
and mechanical. The basic elements of map-scale structure are the geometries of folds
and faults, the shapes and thicknesses of units, and the contact types. This chapter pro-
vides a short review of the basic elements of the structural and stratigraphic geometries
that will be interpreted in later chapters, reviews some of the primary mechanical factors
that control the geometry of map-scale folds and faults, and examines the typical sources
of data for structural interpretation and their inherent errors.
1.2
Representation of a Structure in Three Dimensions
A structure is part of a three-dimensional solid volume that probably contains numer-
ous beds and perhaps faults and intrusions (Fig. 1.1). An interpreter strives to develop
Fig. 1.1. 3-D oblique view of a portion of the Black Warrior Basin, Alabama (data from Groshong et al. 2003b),
viewed to the NW. Thin vertical lines are wells, semi-transparent surfaces outlined in black are faults
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